Field of the Application
The application generally relates to the handling of security mode command, and more particularly, to apparatuses and methods for recovering from security mode command failures.
Description of the Related Art
Due to the growing demand for ubiquitous computing and networking, various cellular technologies have recently been developed, including the Global System for Mobile communications (GSM) technology, General Packet Radio Service (GPRS) technology, Enhanced Data rates for Global Evolution (EDGE) technology, Wideband Code Division Multiple Access (WCDMA) technology, Code Division Multiple Access 2000 (CDMA2000) technology, Time Division-Synchronous Code Division Multiple Access (TD-SCDMA) technology, Worldwide Interoperability for Microwave Access (WiMAX) technology, Long Term Evolution (LTE) technology, Time-Division LTE (TD-LTE) technology, and LTE-Advanced (LTE-A) technology, etc.
According to the 3rd Generation Partnership Project (3GPP) Technical Specification (TS) 36.331, an Evolved-Universal Terrestrial Radio Access Network (E-UTRAN) may activate security by sending a Security Mode Command message which is integrity protected. Assuming that the security activation will not go wrong, the E-UTRAN may subsequently initiate establishment of the Signaling Radio Bearer 2 (SRB2) and Data Radio Bearers (DRBs) before receiving a confirmation of the security activation from the User Equipment (UE). However, there are situations where the Security Mode Command message may not pass the integrity protection check by the UE, i.e., the security activation may fail, which further causes the failure of the radio bearer establishment. In some field trials, the E-UTRAN may not always release the Radio Resource Control (RRC) connection with the UE, as it should, when it knows that the security activation and/or the radio bearer establishment has/have failed.
In such cases, according to the 3GPP TS 24.301, the UE has to wait until expiry of the guard timer of the Non-Access Stratum (NAS) procedure which triggers the security activation. Upon expiry of the guard timer, the UE starts the retry timer and retries the NAS procedure when the retry timer expires. The UE may have to wait for a long time before it can be released from a state wherein it is stocked and cannot do anything. As a result, the user will inevitably experience no service for a long time.